1. Technical Field
The invention concerns a piston ring, with a main body, which exhibits a contact surface, an upper and a lower side surface, and an inner circumferential surface.
2. Related Art
In EP 1 460 318 A1, a piston-ring coating is described, in which at least the lower side surface is coated with a special polymer.
Piston rings execute radial and axial motions in the groove of the piston. These motions cause, among other things, wear on the sides of the ring. Under normal loads, this wear can be counteracted by means of a suitable choice of material for the piston ring. In modern combustion engines, the stress on the ring increases more and more due to higher and higher output, so that exclusive protection of a particular side can no longer be guaranteed via the base material. In this case, an isolated wear-protection layer on the side is needed. A special problem is represented by so-called microwelding as a special type of wear on the sides of piston rings. This phenomenon frequently occurs in Otto reciprocating internal-combustion engines when steel rings are used.
Known procedures which counter ring-side wear are the nitriding of the ring side(s) of steel rings or the thin chroming of the sides, in which nitriding, as has already been stated, is not suitable when microwelding occurs. However, in order to be able to further retain nitrided steel rings to advantage, special protective measures must be considered.